This invention lies in the field of polyethylene piping.
More particularly, this invention lies in the field of large diameter polyethylene pipes for which large angle ells, or large sweeps are required, for turning the pipe through large angles.
In the prior art, it has been known that polyethylene pipe can be joined by taking two lengths of pipe and clamping them coaxially, in end-to-end relation, heating the opposed faces to a selected temperature at which the polyethylene softens to the proper degree, and then pressing the two ends together axially, with sufficient force to cause the softened ends to be intimately fused. See U.S. Pat. Nos. 3,729,360 and 3,846,208. This will provide a permanent weld, which has sufficient strength to match that of the pipe. However, the problem of how to construct angular combinations of polyethylene pipe where the diameter of the pipe was such that it could not be bent, by softening and bending, etc., has not been met, especially for on-the-job field use. Where such angular turns or sweeps were required, it has been customary to use piping of other material, joined to the polyethylene pipe, or the fittings were made elsewhere as a separate item of sale.